Pyrolysis of gaseous hydrocarbons for the production of unsaturated compounds



March 16, 1954 W. W. H PYROLYSIS OF GASEOUS OLLND 2,672,489

HYDROCARBONS FOR THE PRODUCTION OF' UNSATURATED COMPOUNDS Filed July l0, 1948 grave/Wto@ WiL/Holland Patented Mar. 16, 1954 orrlca William Wik HollandQBaltimore, Md.; :in ssig'norI to' The Gyro ProcessCompany,- Detroit, Mich., afl

corpratinof: Michigan Amalia:ation-July310, 1948,.v Serial'No'.- 38,153

1 cisimf (c1. 26o-683) This-:invention directed to Athe pyrolysis of hydrocarbons, and more `particularly vtoeictin'g the -molecular decomposition. oi normallygaseous hydrocarbons by .the-applicationofheat 'in order to-increase their commercial ifalueandfndustrial usefulness. v

.Large quantities y of gaseoushydrocarbons. are collected currently. from :the casingheads A.of foil Wells,- .fromf natur-algas lWellsVand "aroundfpetro leumrefineriesas-va'by-product of f distillation and cracking operations 11i-relatively .smalllportion offgthe gases .gatherediromihesesources is. .processed for -zthe 1productienwof more valuable materials, While enormous amounts are .inaisense wastefullyf burned; as :rfdomestic A and industrial fuel.;l

It 'is therefore- 'an'.object '-,ofvthis .invention to provide Leconomic .means adapted kto the profitable 'molecular f decomposition or reconstitution of-. suchA f gaseous. hydrocarbons, whichaare 7 pri:- marily r of l`.the saturated ,type, andAL their-conversiorr into-unsaturatedhydrocarbons usetulrinlthe eldof'chemicalfsynthesia In-.thefnormal operation-ofecracking processes it is customary to employ liquid charging stocks suchas reducedcrudgas .oilyvkerosene fractions orf:the.=like, theqdesired-Jend-L product, beingiprimarilyn-motor -fuels yof Vv,one type-or another. In such: operationsV a-.minimumg.produation` or ,gases ous f/fractions. ris-devasirableaFurthermore;` inth'e manufacture of` ymotor ifuelsyitA-lis' rcustomaryo talsefadvantagev oftevery, practicalaneans of 'recoveringA liquid `fractions:iromf thegasesn through the employment :off operationsl--suchQas compr-es siem? cooling; absorption;rpolymerization;etc.,in order@ to obtain!v the y-.-metximum `:.yieldaof liquid products.v However,- when:,.craclgig;l gaseous, hy.-

dro-carbons the reverselgcondition obtains sincelit isfdesirable:torrecever:theamaximumbuantityof gaseous iczroducts.:Withaminimumy liquid; yieldr .v

While the pyrolysis-fso{normally gaseousohyf drocarbonswis --notfnewvito the artfvgthefextent to Whichf iti is i employed int :the .petzunleinrnn industry cannot be compared withL-the scvalejupon;` which liquidr fchargingcstocks fare lcraclgzc da, .Nevertheless; developments-within :recentY years 1in `thefield offsynthetics havendemonstrated thefnecesstyof anfsabundant .supply/'Tof funsaturatedrdiydrocarbonscfromiv :which suchl.,m`ateria;ls fcan-be.made, andHthefpetrolemn'-` derivativesrfurnishlthe natu.. ralaandcheapestsource ofy'supply.

Until recently unsaturated hydrocarbons were obtainedrlargely @from thefdecompsitionmfyaleohoLlbut ths'isituati'onhas 'beemreversedrand-.the

2i hydrocarbons" derived" from petroleum.` This chemical aspect ofthesituation has directed attenti'on'to the'pyroly'sis of gaseous hydrocarbons for 'the production` of unsaturated compounds from' Whichlavariety of' useful materials can be made, notablyA plastics, lacquers, gums, resins, alcohols', rubber; anti-knock and anti-freeze compounds and'kindred products, all of which are finding Vready and increasingly Wide commercial'application: u

While considerable progress has been made in synthesizingvarous materials from unsaturated hydrocarbons, it is'believedthat the `potentialities .of `this eld "have scarcely been touchedbecause'of the absence of 'an' abundant and cheap source. of' supply 1 of unsaturated hydrocarbons, andsince Vthe 'supplyh'as been limited in the past, furtherdevelopments 'in the manufacture of synthetics will'be governedlargelyby ,thel availability and cost of unsaturated hydrocarbons in f the future."

It isthereforea 'further object 'of `this invention toprovide 'means whereby unsaturated hydrocarb'ons' can be' produced in any desired amounts and'npon! an" economic 'basis which will be inviting'to'the"manufacturers of synthetics.

In' accordance with'this invention, the gas col'- lected aroundoif fields, petroleum reneriesor from natural gas wells or other sources, is passed through the 'heating -zone of' Aa suitably designed furnace Whereinit'is decomposed or molecularly reconstituted into agaseous fraction consisting primarilyof :unsaturatedhydrocarbons and a heavier fraction composedl'largely of aromatic hydrocarbons.` Thelatter; together with some liquid para'lnic' fractions Within the motor fuel boiling range, are produced as a result -of polymerizati'on' vreactions which' proceed concurrently with the deoomposition'reactions. l

After separating the gaseous constituents and heavier components by` fractionation or other- Wise, theliquid fraction"maybe Withdrawn and further processed `4for the production of high anti-knock'motor fuel, or it maybe returned to the system'witli the lraw'feed, which lis also lin liquid form after. havingV *been compressed and cooled-below its condensationtemperature. The choice .of' returning 4the `liquid fraction tothe system .for reprocessing `in-order to increase the yield cnf-.unsaturated .gaseous hydrocarbons, or divert'- ing .it to .motor fuelg is. governed by the relative .market requirements.-

While nltl'iisjivention is-directed specically to amolgcaremam439mg,gngdegipmgmnsaturatedf. 'thepyrolysis' of. gaseous hydrocarbons for the production of unsaturated compounds, the same general principles may be applied when cracking liquid hydrocarbons in the vapor phase for the production of high anti-knock motor fuel. The essential difference between the two operations is that in the pyrolysis of gases, unsaturated gaseous compounds is the primary end product desired, with a relatively small production of liquid hydrocarbons as a by-product; while in the cracking of liquid hydrocarbons for motor fuel, gaseous hydrocarbons are obtained as a Toy-product. The two are further distinguished by the wide difference in the operating temperatures. When cracking liquid hydrocarbons in the vapor phase temperatures of the order of l000 to 1250 F. may suiice to effect the desired decomposition of most charging stocks, while in gas pyrolysis the temperature may reach 1600" F.

For a further understanding of this invention reference is made to the following description and the accompanying drawing forming a part of this specication, wherein suitable apparatus and equipment for carrying out the several steps of the process are shown diagrammatically.

Referring more particularly to the drawing, numeral I designates a supply of hydrocarbon gas which when obtained from the casinghead of oil wells or from natural gas wells is, largely saturated in character and is composed primarily of methane, ethane, propane and butane. If the gas is collected from the various sources around an oil refinery employing cracking stills it will contain, in addition to the above constituents, some unsaturated hydrocarbons such as ethylene, propylene and butylene derived from the cracking operation, the proportion of such unsaturated hydrocarbons present in the total gas being governed by the extent to which cracking is employed in the particular renery. However, the presence of unsaturated compounds in the gaseous charge is not objectionable, and may be considered desirable, since they are handled along with and in the same manner as the saturated gases. Whether or not they enter into the decomposition and polymerization reactions within the conversion zone is of little importance since the overall result is practically the same, either in the presence or absence of the unsaturates in moderate amounts, which is usually a relatively small proportion of the total gaseous charge, averaging perhaps five to fifteen per cent.

The gaseous charge passes through line 2 to a compressor 3 wherein it is compressed to approxi.- mately 250 pounds per square inch gauge. Leaving the compressor, the compressed gas passes through a cooler i where it is largely liqueiied, and thence to an accumulator 5. The uncondensed portion of the gas, consisting mainly of hydrogen and methane, is withdrawn from the top of the accumulator through line 5, controlled by valve 1, and sent to the plant fuel gas-burning system. The liquefied gas collecting in the bottom of the accumulator is withdrawn through line 8, controlled by valve 9, and delivered by pump It to a gas pyrolysis or cracking coil I I located in a furnace I2, red by burners I3. The mixture of hydrocarbon gases is decomposed in this coil under temperature conditions within the range of 1300 to 1600 F., and under a pressure not in excess of approximately 300 pounds per square inch gauge. Steam is admitted to the cracking coil as an effective corrosion preventive agent.

The decomposed hydrocarbons leaving the cracking coil through line It enter a temperature arrester I5 wherein the temperature of the gases is substantially instantaneously reduced to a degree below that at which further decomposition can take place. This is accomplished by direct and intimate contact between the hot gases and an atomized liquid cooling agent which is preferably produced within the system as hereinafter described, thereby reducing the temperature to approximately 600 F.

In the pyrolysis of gaseous hydrocarbons under the prevailing high temperature conditions required, both the decomposition and polymerization reactions proceed with such velocity and are completed Within such a short interval that it is difcult if not impossible to control the reactions to an extent which will avoid altogether the formation of some tarry substances and finely divided carbon which, if not segregated and removed from the system, will deposit upon the inner walls of the transfer lines and collect upon the fractionating trays in the bubble tower, eventually fouling the system and resulting in premature shutdowns for cleaning purposes.

I have found that while it is extremely difcult to avoid completely the formation of resinous materials and sooty coke in gas pyrolysis operations, their presence may be reduced to a negligible quantity if certain precautionary measures are followed. I have noted also that the formation of such materials is not altogether a result of the decomposition reactions per se, as is generally believed, but is due largely to the method of checking the reaction by direct contact with a cooling agent after decomposition has been effected to the desired degree.

Uniform operating conditions of time, temperature and pressure are of primary importance in gas pyrolysis operations, but regardless of the regularity attained in these conditions, resins and coke will be formed in the quenching step unless the arrester temperature is also maintained at a substantially constant level. Widely fluctuating temperatures in the arrester result in coke formation for the same reason that coke collects at unilnrotected and exposed spots in insulated hot oil nes.

In order to prevent such temperature fluctuations the arrester is maintained at a constant temperature under thermostatic control by means disclosed in my pending application, Serial No. 765,438 which in substance comprises automatically controlling the iiow of quenching oil to the arrester, in response to the temperature fluctuations therein. Means are also provided in the above application for keeping the mixture of oil and gas in a constant state of agitation while passing through the transfer line IB leading to the separator I'I, by inserting a helical vane I8 in the line which imparts a rapid swirling motion to the materials and thereby effectively retarding the deposition of solids upon the inner walls of the line.

The severity of gas pyrolysis temperature conditions appears to render impossible the complete absence of dust-like coke in such operations, as well as the formation of small amounts of tarry substances which apparently result from polymerization reactions which accompany those of decomposition. However, the presence of such materials in the small amounts formed present no particular problem since they may be separated from the other decomposition products and diverted from the system. To this end the mixture of liquids, solids and gases, leaving the arrester in a state of turbulence which will not permit the-deposition of coke atthis point, passes @www throughtlinehlx at a hi'ghfvelocitw andient'ers'. the separator- I 12 "wherein1 the: velctity isi greatlyf'rerduced, permitting: the -sol-idsj and resin'ouszmaterials'- to settleto the bottom, while the-gases*` and lightA fractions -.are removed-*with 'the' A*aid of steam.- The solidsE and- UheavyTi materialsf are then withdrawn f `through line I i9, loorrtrolledi'-v by: `valve and diverted'from the-system;`

The overhead. products from this i "operation leave:the separator throug-hylinel 2l2tandenter the fractionating tower^-2-l wheres further separa*- tion iseected primarily into gaseousand liquid products, aV tempera-ture-gradiant ofwapproximately 4509 tov `25o-"115V'beingmaintainedwithin thetower, while steam'w is @injected i'nt'o'-4 thelower sectionto -assistin--th'e sepa-ration: In ordepto controlthe mid1tower-temperature;, a' 'stream of reux oil, Ais Withdrawnirom anrintermediate pointN through` line^ v23; controlled by valve 24, passedthrougha cooler 2,5 .andcollected in a working tank 26. product of a relatively constant boiling point range, -this continuous andfeabundant supplyfpf oil serves the, dual purpose; of. controlling.. the tower temperature, and also quenchingr the; high temperature decomposition products enteringthe arrester.- A portion offgthe oil is:withdrawn .from thel working tank vby,purnpvfZiand delivered through line 21 Vto theuppersection of the tower, Controlledv by. Valve 28,.' r Anotherwportionzis withdrawnbr pumpmza and., delivered through' line 3i), partially controlled by;- valvef 3 I to theA .spray nozzles 32 located in the top of the arrester, as a quenching medium.

The arrester is maintained under constant temperature conditions of approximately 600 F., under thermostatic control, as fully described in my pending application, Serial No. 765,438, now U. S. Patent No. 2,608,527, the mechanical means for automatically admitting the regulatory iiow of oil through the by-pass 33 consisting essentially of a valve 33' actuated by a motor, a magnet or other suitable device electrically controlled by the make-and-break contact of the thermostat 34 connected through a conduit 35 with a source of current (not shown) and said device. Valve 33 may be magnetically actuated to the open or closed position as the thermastatic circuit is established or broken by the rise or fall of the temperature in the quenching chamber. The thermostatic element 34 inserted through the wall of the chamber is electrically connected with the magnets 35 through conduit 35 Iand with a source of current (not shown) in such a manner as to control the movement of the valve mechanism 33' to the open or closed position in response to theuctuation of temperature in the chamber. When the temperature rises above the desired point, valve 33' is opened automatically, admitting more oil to the chamber; when the temperature falls, the valve is closed, diminishing the flow of oil, thus maintaining an even temperature in the quenching chamber.

In the initial operation of the gas pyrolysis system herein described it is necessary to prime the fractionating tower with a suflicient quantity of oil, preferably a naphtha cut of approximately 300 to 400 F. boiling range, for temperature control and quenching purposes, but thereafter condensation of a part of the products of decomposition and polymerization are more than suicient for these requirements and there is a gradual but slow accumulation of oil in the system. 'I'he excess of oil may be Withdrawn from the bottom of the fractionating tower through Being a clean, carbon-free' 135, 'co'ni'.rnlledfL by vaive'si 313 ndlfii fand Inra ther processedforfhighmntiaknnclcmotmfuel'or it :may bei .returnedto this feeduaccumulatorrjby pump. 438; ithroughflirre.39;..controtled2doyt valves 31S and 40;: `and .agaizrfdecomposedvror.rthzaspro: duction .of a'dditibnalsunsaturatedigasenusdydr carbonsi.`

The.l overheadz` leaving: fthef topcofz the' traction ating: tower: through. line cMs .passes-:through ra cooler 42 and into a gas-liquid separatnrlatlie liquid: accumulating.;- ir theL bottom' oftthefsepar-ator .being rlargely aromatic.dnsnharacterx'. A portion rof this liquid is-:returned'tothe topoflth tower asia remix-temperatnrecontrolhnedinrby means :aofi pump?. 4 5 ,'-J-.throughe linellcicontrolldrby valvef f The` :gaseous-f` products: leaving.' fthe; top:1or;th'e separatorfthrough linel44rcontrolledibyfvalvef consistena.mixturefofsaturatedandlunsaturated hydrocarbons-f. composed: primarily of .Ccland C4 compounds. 'Ihis gaseous mixture is sentito a gas separating system Iwhere?separatioi'rl is efeotedzinto its' componerrtzparts.- by? ways and m'eansfwell: known to. the art utilizing-:suchimethi od's-aszarezadaptedltoth'elrecovery of thedesired constituentsm- Initsfi'simplestform'rand by' way.J of; illustration only; vSuchx an operationy consists-2in1; rst'fl com pressing the'A gas -forf the recoveryof liquidfra-c2- tions; r The gas passing through`v fling 44r fi-tex= ample, f is L conductedtovv al gashY compressionf plant 48?, operating preferably inf la1-'succession#offfinl-I creasingly highery pressure stages? combiiled"i-vvith intermediate cooling between the stages. The uncondensed gases leaving the compression plant through line 49 go to an absorption tower 53, maintained at approximately the same pressure as that employed in the highest compression stage, usually between 200 and 500 pounds per square inch gage.

The liquid withdrawn from the Vbottom of the gas-liquid separator 43 through line 5|, controlled by valve 52, is delivered by pump 54 to the top of the absorption tower as an absorption medium for extracting iso-butylene and buta-A diene from the gases because of their greater affinity for aromatics than the other C4 compounds, i. e., normal butylen'e and butane.

The enriched aromatic liquid withdrawn from the bottom of the absorber through line 55, controlled by valve 56, together with that withdrawn from the compression plant through line 50, is delivered by pump 51 to a fractionating column 58 equipped with suitable fractionating plates (not shown) and a reboiler 59, wherein the isobutylene and butadiene fractions are recovered as an overhead product, while the aromatic liquid is withdrawn from the bottom of the fractionator through line 60, controlled by valve SI. This liquid may be further fractionated to remove the parainic hydrocarbons liquefied in the compression operation, the aromatics then being recovered as nished product.

The overhead :products leaving the absorber 53 through line 62 are processed in suitable apparatusshown diagrammatically at 63 for the removal of water and carbon dioxide by the action of reagents such as calcium chloride and silica gel. The remaining gases are then passed consecutively through a compressor 64, a cooler 65 and into a low temperature fractionator 66, preferably of the bubble tower design, also equipped with a reboiler 68. This fractionator is maintained under a pressure of about 500 to 1000 pounds per square inch gage. and at a temperature of about 90 to 175 F. Reflux for the top of the tower is provided by cooling and condensing a, portion of the overhead product in a reux condenser 61, through which a suitable rei'rigerant, such as, for example, expanding liquid ethane or propane, is passed. An additional cooler 69, of a similar type is provided to further condense the overhead product which is collected in a receiver 10, and which consists essentially of ethylene.

The liquid products Withdrawn from the bottom of the fractionator through line 1|, controlled by Valve T2, consisting primarily of ethane and C3 and C4 hydrocarbons, of both the saturated and unsaturated types, may be further fractionated by similar methods for the recovery of other unsaturated constituents such as propylene and butylene, as will :be apparent to those skilled in the art, the remaining saturated hydrocarbons being returned to the feed for reprocessing.

What I claim:

A process for refining hydrocarbonacomprising: thermally converting normally gaseous hydrocarbons of the saturated methane series type into those of the unsaturated ethylene series type, passing gaseous and light liquid hydrocarbons constituting products of such conversion through a primary fractionating zone, removing converted gaseous hydrocarbons as an overhead product from th'e fractionating zone and liquid hydrocarbons from the bottom of said zone, cooling the overhead hydrocarbons removed from the top of said fractionating zone and passing the same through a separating zone, effecting in said separating zone a `separation of gaseous hydrocarbons from a low-boiling liquid aromatic fraction, compressing the gaseous hydrocarbons discharged from said separating zone and passing the same through an absorber, delivering the aromatic liquid fraction to the top of said absorber for countercurrent now relationship to the ascending compressed unsaturated hydrocarbon gases, whereby to cause the aromatic liquid hydrocarbons to absorb and remove selectively from the contacted gases iso-butylene and butadiene, fractionating the last-named liquid hydrocarbons to separate iso-butylene and butadiene as overhead products, and treating the hydrocarbon gases removed from the top of said absorber to recover lethylene therefrom.

WILLIAM W. HOLLAND.

References Cited in the file 0f this patent UNITED STATES PATENTS Number Name Date 2,168,610 Schutt Aug. 8, 1939 2,230,219 Carey Feb. 4, 1941 2,263,557 Greenewalt Nov. 25, 1941 2,340,778 Steward et al Feb. l, 1944 2,346,642 Babcock et al Apr. 18, 1944 2,367,479 Wolk Jan. 16, 1945 2,378,057 Dorsett et al June 12, 1945 2,431,485 Keeling Nov. 25, 1947 2,498,806 Hachmuth Feb. 28, 1950 

